1. Field of the Invention
The present invention relates to an optimization method for a code division multiple access (CDMA) system, and more particularly, to a method for optimizing forward link coverage in a CDMA network.
2. Description of the Related Art
To optimize a CDMA system, it is desirable to conduct basic base station tests to optimize the coverage areas serviced by the base station, the hard handoff performance between exchanges, the call quality and the location-registration success rate. Coverage optimization is categorized into forward link coverage optimization and reverse link coverage optimization.
When setting up base station equipment to establish a desired coverage area to be serviced, conventional methods expand/contract the coverage area simply by increasing/decreasing the radio frequency (RF) power of the pilot signal transmitted from the base station. Coverage area expansion is necessary when the forward link coverage is less than the reverse link coverage; coverage area contraction is necessary for the opposite condition.
To further adjust the actual coverage area, adjustments to the base station antenna are made conventionally. For instance, the height of the antenna on the base station tower can be adjusted relative to the height of neighboring buildings. The antenna beam tilt may be adjusted to improve the signal strength in a certain region, or, to expand or contract the overall coverage area when adjustments to the base station output power are insufficient to do so.
In addition, measures can be taken to reduce interference resulting from an excessively large handoff area between two neighboring base stations. The antenna beam tilt can be adjusted by as much as three to five degrees to reduce the coverage area, and hence, the handoff area, to thereby remedy the interference problem. Moreover, to increase the receive signal strength from mobile stations in the reverse link, the azimuth direction of the base station antenna can be adjusted, particularly in an urban area to improve service.
While the above techniques may optimize cell coverage to a first order, there is a need for an improved coverage area optimization method which is more rigorous in taking into account real world environmental conditions. The present invention addresses this need.
The present invention is intended to provide a method for optimizing forward link coverage in CDMA network.
The present invention pertains to a method for establishing appropriate coverage per base station in a CDMA network, a method for establishing a basis for determination of coverage per base station in CDMA network, a method for establishing coverage per base station by adjusting system parameters and a method for performing cell coverage optimization of a CDMA network.
In one aspect of the invention, there is provided a method for optimizing forward link coverage in a spread spectrum communication system, e.g., a CDMA system. Spread spectrum test communication signals are transmitted from a base station at a known power level, using an antenna having a known beam direction. Orthogonal channel noise is simulated in order to model noise generated by wireless communication traffic existing in an operational communication system of many subscribers. A mobile station receives the test communication signals in a specific region of a cell area to be serviced by the base station, and measures signal quality parameters, e.g., RSSI, EC/Io and a forward frame error rate (FFER), from the received signals and simulated noise. The measured signal quality parameters are compared to respective criteria. Each region of the cell is designating as being satisfactorily covered by the base station if the measured signal quality parameters substantially satisfy the criteria. Otherwise, base station equipment is adjusted to modify the transmission of the test communication signals, and the process is repeated.
Other objects and advantages of the invention will become apparent upon reading the detailed description and upon reference to the drawings.